The
importance of alkoxy radicals (RO·) in atmospheric chemistry is well known. They
are key intermediates in the oxidation of hydrocarbons. In our lab, alkoxy
radicals are studied by laser-induced fluorescence (LIF) spectroscopy, with both
medium and high resolution.

The alkoxy
radicals are generated in a supersonic free jet expansion by UV laser photolysis of the corresponding alkyl nitrites (RONO). The moderate-resolution
(mod-res, FWHM ~0.1cm-1)LIF
spectroscopy allows us to record vibrationally resolved spectra of the alkoxy
radicals, as well as to measure their fluorescence lifetime, while the
high-resolution (hi-res, FWHM ~200-300MHz) LIF spectroscopy is be able to provide us with rotationally
resolved spectra.

Schematic
diagrams of the moderate- and the high-resolution experimental setup are shown in
Figure 1 and Figure 2, respectively.

So far, LIF spectroscopy of primary alkoxies
(containing up to 12 carbon atoms), secondary alkoxies (containing up to 7
carbon atoms), and cyclohexoxy has been studied in our group. A
full list of the alkoxy radicals that we have studied is available. As an
example, the moderate- and high-resolution LIF spectra of 1-propoxy (C3H7O·)
are given in Figure 3 and Figure 4, respectively.

Rotational analysis has been done by simulations
and eventually fits using the graphical interface program
SpecView. Different
rotational structures can be assigned to different conformers. Simulations of
Band A and Band B of 1-propoxy are shown in Figure 5. They are assigned to G-(gauche-,
) and T(trans-,
) conformers,
respectively. Details can be found in Selected Publication1 and 2.

Most recently, we improved the calibration system
in our high-resolution LIF setup by introducing Doppler-free absorption
spectroscopy of molecular iodine. Accuracy of ~50MHz has been obtained. The
experimental setup is shown in Figure 6 and one example of methoxy radical
(showing the spin-rotation splitting) is given in Figure 7.

When combined with other spectroscopic
techniques, LIF spectroscopy can be even more powerful. Figure 8 and
Figure 9
show the experimental setup of Dispersed Fluorescence Spectroscopy (DF) and
Fluorescence-Depletion Infrared Spectroscopy.